Beach sand needs to be baked, iirc. Set an oven to 300 and leave in for two hours. Don’t remember where I read that but it’s stuck with me for years.
Interesting, I never heard that. I never really had issues with my sand. I am guessing the heat "hardens" the grains or something.
Kills the things living in it. Since you've had it a long time in presumably a sealed box, I suspect age has accomplished much the same thing!